1. Field of the Invention
The present invention relates generally to a piezoelectric sensor for monitoring kinetic momentum of movable mechanical constructions. More specifically, the invention relates to a piezoelectric-type momentum sensor suitable to use as an accelerometer, such as that employed for an automotive control system. Further the invention relates to a piezoelectric sensor specifically adapted for monitoring relative displacement between a vehicle body and a wheel axel in an automotive suspension system.
2. Description of the Background Art
The U.S. Pat. No. 4,696,489, issued on Sept. 27, 1987, to Takeshi FUJISHIRO et al, and assigned to the common assignee of the present invention discloses an automotive suspension control system in which an accelerometer is incorporated for monitoring vertical acceleration of the vehicle body. The monitored vertical acceleration of the vehicle body is utilized as one of the control parameters in controlling damping characteristics of the vehicular suspension system. In the construction shown in the aforementioned U.S. Patent, the accelerometer employs an inertial member causing deformation of a resiliently deformable member and a strain gauge for detecting deformation magnitude and speed and whereby detecting the vertical acceleration of the vibrating vehicle body. This type of accelerometer may be replaced with a piezoelectric-type accelerometer for performing the same or similar acceleration monitoring operation.
One of the typical constructions of piezoelectric-type accelerometers which employ a piezoelectric element as a sensor element, has been disclosed in the Japanese Patent First (unexamined) Publication (Tokkai) Showa 59-23223, for example. This conventional piezoelectric accelerometer employs a piezoelectric sensor element supported in a housing in cantilever fashion. In this construction, the piezoelectric sensor element may vibrate about the one supported end when vibration energy is exerted. This causes the concentration of distortion stress around the supported end and results in fatigue or uneven exhaustion. Therefore, such concentrated stress may make it difficult to stably maintain reasonable performance and may shorten the life of the accelerometer.
In addition, when the supporting structure, supporting the, piezoelectric sensor element, is asymmetric in construction, the sensitivity of the sensor element tends to be fluctuate depending upon the exerting direction of the vibration energy. In order to avoid this, it has been required that the conventional cantilever type piezoelectric sensor element supporting structure be precisely symmetric in construction. This requires high accuracy machining, such as by of laser machining apparatus. Such high accuracy machining requires substantial cost.